1. Field of the Invention
The invention relates to a fan system, and more specifically to a fan system capable of stopping a motor thereof.
2. Description of the Prior Art
With increased functionality of electronic products, it is important to dissipate heat generated thereby. Typically, a fan system is utilized to dissipate heat from electronic products. When the power of the electronic product, which the fan system is applied to, is turned off, or no more power input into the fan system due to the separation from the electronic device physically, the motor of the fan system may continue to rotate due to inertia, which causes danger to users if they touch it. Further, resumption of power or reconnection of the fan to the electronic product causes a waiting time, which decreases efficiency.
FIG. 1 shows a fan system 1 having an energy storage apparatus 10, a small signal power 20, a driver 30, a motor 40 and a selecting device 50. The energy storage apparatus 10 is electrically connected to a power supply 2 which may be built into an electronic device and includes a storage capacitor CE for receiving power from the power supply 2. The small signal power 20 is electrically connected to the energy storage apparatus 10 for receiving power from the power supply 2 and converting accordingly to output converted power. The driver 30 is electrically connected to the small signal power 20 and receives power therefrom to generate a driving signal P so as to drive the motor 40. The motor 40 is electrically connected to the energy storage apparatus 10 for receiving power and the motor 40 is also electrically connected to the selecting device 50 so that the selecting device 50 determines whether to output the driving signal P to the motor 50. The driving signal P may be a pulse width modulation (PWM) signal generated by the driver 30 and allows the motor 40 to rotate when the driving signal P is input into the motor 40. Further, the fan system 1 has a first capacitor C1 and a second capacitor C2. One end of the first capacitor C1 is electrically connected to the small signal power 20 and the other end thereof is electrically connected to ground. One end of the second capacitor C2 is electrically connected to the energy storage apparatus 10 and the motor 40, and the other end thereof is electrically connected to ground.
The fan system 1 has a power path and a control path. From the energy storage apparatus 10 to the motor 40 via the second capacitor C2 forms the power path, and from the energy storage apparatus 10 to the motor 40 via the small signal power 20, the driver 30 or the first capacitor C1 forms the control path. When the fan system 1 receives power from the power supply 2, power is obtained to the motor 40 via the power path and the driving signal P for the motor is obtained via the control path. However, once the power supply 2 is turned off or the fan system 1 is separated from the power supply 2, no more power is obtained, and the storage capacitor CE of the energy storage apparatus 10 releases power into the control and power paths, so that the first capacitor C1 and the driver 30 receive power released by the storage capacitor CE. Then, the first capacitor C1 generates a start-up signal S to the selecting device 50. The selecting device 50 outputs the start-up signal S to the motor 40 and forms a short-circuit loop in the motor 40, and thus an induction current is generated in a coil L of the motor 40 due to inertia after power disconnection so that a magnetic field in an inverse direction is generated to stop the inertia rotation of the motor 40.
However, in practice, when the storage capacitor CE releases power, the driver 30 also receives power to generate the driving signal P to the motor 40 at the same time. Since both the first capacitor C1 and the driver 30 are on the control path, the timing input to the selecting device 50 and potential of the start-up signal S and the driving signal P are very close. Hence, the selecting device 50 may determine to select the driving signal P instead of the start-up signal S so that the stopping function for the motor 40 can not be performed normally.
Moreover, since the control path has two branches (through the first capacitor C1 and the driver 30), the capacitance of the storage capacitor CE must be enough large so as to provide enough power to the power and control paths. However, this is more expensive and the production costs are increased.